Automated material handling system for a manufacturing facility divided into separate fabrication areas

ABSTRACT

An automated material handling system is presented for a manufacturing facility divided into separate fabrication areas. The automated material handling system plans and carries out the movement of work pieces between fabrication areas and maintains a database indicating the location of each work piece within the manufacturing facility. In one embodiment, the automated material handling system accomplishes the containerless transfer of semiconductor wafers through a wall separating a first and second fabrication areas. The wafers are transported within containers (e.g., wafer boats). The material handling system includes a number of transfer tools, including air lock chambers, mass transfer systems, robotic arms, and stock areas. The material handling system also includes a control system which governs the operations of the transfer tools as well as the dispersal of containers. The air lock chambers provide isolation between fabrication areas while permitting the transfer of wafers between the fabrication areas. A mass transfer system positioned within each air lock chamber allows for containerless transfer of wafers through the air lock chamber. The stock areas provide storage areas for containers adjacent to the air lock chambers. The robotic arms are used to move containers between the stock areas and the air lock chambers. The control system includes a main processor, a remote processor associated with each fabrication area, an internal network transmission medium coupling the main processor to the remote processors, and a cell network transmission medium within each fabrication area coupling the corresponding remote processor to one or more transfer tools.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to material handling systems and in particular toan automated system for the movement of work pieces within amanufacturing facility.

2. Description of the Relevant Art

Manufacturing facilities often employ material handling systems to movematerials in various states of production (i.e., work pieces) betweenprocessing locations. Production states of work pieces vary from rawmaterials to finished products. Containers or carriers are commonly usedto move the work pieces from one processing location to another duringthe manufacturing process. Typically, a transportation system isemployed (e.g., a conveyor belt system) for moving the containers fromone processing location to another within the system. Work pieces aretypically placed into containers, and the work-piece-containingcontainers are transported between processing locations. Needed emptycontainers are generated as work pieces are removed from containers inorder to be processed.

An example manufacturing facility is one which fabricates integratedcircuits on semiconductor wafers. Such a facility typically includes aplurality of wafer fabrication process tools which perform variousfabrication process steps upon groupings of semiconductor waferscalled"lots". Each process tool typically has an accompanying stock areafor storing containers of wafers waiting to be processed by the tool aswell as wafers having already been processed by the tool. A commonexample of such a container is a wafer cassette or"boat" adapted forholding one or more semiconductor wafers.

Chemical mechanical polish (CMP) techniques are increasingly employed inthe fabrication of integrated circuits. CMP techniques are used toplanarize exposed upper surfaces of dielectric layers formed betweenlayers of electrical conductors (i.e., interconnects). CMP combineschemical etching and mechanical buffing to remove raised features on theexposed upper surfaces. In a typical CMP process, a semiconductor waferis mounted on a rotating holder and lowered onto a rotating surfaceflooded with a mild etchant solution, generally defined as a silicaslurry. The etchant grows a thin layer on the exposed wafer surface thatis almost simultaneously removed by the buffing action. The net effectis a very controlled polishing process capable of incredible flatness.

One problem with CMP techniques is that they produce large amounts ofcontaminants, including particulates, metallic ions, and chemicalsubstances. The destructive effects of those contaminants is readilyapparent in the overall performance of VLSI or ULSI devices. Anycontaminants attributed to the slurry, chemical reactant, or buff/etchbyproduct, which is thereafter introduced into other fabricationoperations, severely compromises the success of those operations. Forexample, ingress of contaminants from the CMP operation to the thermalfurnaces used for growing oxide, or to the chambers used for implantingions, would negatively impact the resultant grown oxide or junctionprofile.

Without adequately preventing deposition of CMP-derived contaminants onsemiconductor wafers undergoing other fabrication operations, CMP cannotbe successfully employed. One way to minimize deposition of CMP-derivedcontaminants on semiconductor wafers undergoing other (i.e., non-CMP)fabrication operations would be to perform the CMP process in an areaisolated (i.e., hermetically sealed) from other fabrication areas.Maintaining separate the CMP area from the other fabrication areasbegins by installing a wall between those areas. Wafers must, however,be transported between the respective areas so that CMP can beincorporated within the process flow.

Transport of wafers between CMP and non-CMP areas entails passing thewafers through a door separating the areas. The door, depending uponsophistication, can be a load lock chamber adapted for passing awafer-containing container. The wafer or wafers are transported in thecontainer through the chamber from one area to another area. The loadlock comprises an air circulation and filtration system whicheffectively flushes the ambient air surrounding the wafers.Unfortunately, however, the load lock by itself cannot in most instancesremove contaminants from the surface of wafer-containing containers. Thecontainers pick up contaminants while in the CMP fabrication area. Whenthe containers passes through the load lock unit, those contaminants arenot always flushed from the containers in the load lock. As a result,containers passed from one area to another may have contaminantsclinging to them which may come loose and find their way onto thewafers.

It is therefore desirable to minimize the opportunity for a contaminatedcontainer to pass to and from a CMP area. An effective method ofpreventing passage of container entrained contaminants into what shouldbe a "clean room" environment from a relatively dirty CMP room is topass only the wafers through the wall and not the containers in whichthey reside. Such wafer transfer systems require coordinated efforts onboth sides of the wall.

Robotic arms are now available which are able to accomplish many tediousand repetitive tasks previously performed by humans. Unlike a human,however, a robotic arm tirelessly performs such a task the same wayevery time, reducing variability in both the end result and the amountof time required to accomplish the task. The use of one or more roboticarms in a manufacturing process thus adds an element of predictabilityto the process.

Typically, if an empty container is not available when needed by aprocess tool, an empty container must be transported from anotherlocation in the system. Transportation of the empty container requirestime, causing a delay in the processing of a wafer lot. Such time delaysresult in inefficient use of the process tool. The cumulative cost ofsuch time delays may be substantial in a large semiconductor fabricationfacility having several process tools which are costly to purchase,operate and maintain.

An obvious solution to the problem is to provide a relatively largenumber of empty containers in order to minimize the delay times. Thissolution may be prohibitive, however, both in terms of initial containercosts and container storage costs. An increased number of emptycontainers requires more and/or larger stock areas for storage, and doesnot necessarily reduce the number of required container moves orincrease production efficiency. Adequate distribution of the containersmust be accomplished such that a sufficient number of empty containersare available when and where they are needed.

It is therefore desirable to have an automated material handling systemfor a manufacturing facility divided into separate fabrication areas.Such an automated material handling system would plan and carry outautomated wafer transfer operations designed to pass only work pieces(e.g., semiconductor wafers) through walls separating fabrication areas,and not the containers used to hold the work pieces. Automating thewafer transfer operations would reduce the variability characteristic ofmanual operations. The desired automated material handling system wouldalso manage the distribution of empty containers within themanufacturing system. Adequate distribution of empty containers wouldreduce the total number of empty containers required, reduce the numberof required container moves within the system, reduce the requirednumber and/or sizes of stock areas, and increase the overall productionefficiency of the manufacturing system.

SUMMARY OF THE INVENTION

The problems outlined above are in large part solved by an automatedmaterial handling system for a manufacturing facility divided intoseparate fabrication areas. The automated material handling system plansand carries out the movement of work pieces between fabrication areasand maintains a database indicating the location of the work pieceswithin the manufacturing facility. In one embodiment, the automatedmaterial handling system accomplishes the containerless transfer ofsemiconductor wafers through a wall separating a first fabrication areaand a second fabrication area. The semiconductor wafers are transportedwithin containers (e.g., wafer cassettes or "boats"). The materialhandling system includes a number of transfer tools, including one ormore air lock chambers, mass transfer systems, robotic arms, and stockareas. The material handling system also includes a control system whichgoverns the operations of the transfer tools as well as the dispersal ofcontainers within the manufacturing facility.

The air lock chambers are located within sealed openings in the wall,and provide isolation between the first and second fabrication areaswhile permitting the transfer of semiconductor wafers between thefabrication areas. A mass transfer system positioned within each airlock chamber allows for the containerless transfer of wafers through theair lock chamber. The stock areas provide storage areas for empty andwafer-containing containers adjacent to the air lock chambers. Therobotic arms are used to move containers between the stock areas and theair lock chambers.

The control system includes a main processor, a remote processorassociated with each fabrication area (i.e., cell), an internal networktransmission medium which couples the main processor to the remoteprocessors, and a cell network transmission medium within eachfabrication area which couples the corresponding remote processor to oneor more transfer tools. Each network transmission medium may be, forexample, a multi-conductor cable, a coaxial cable, or a fiber-opticcable. The main processor receives messages from a host processor via anexternal network transmission medium. The main processor produces one ormore transfer commands in response to each message directing a wafertransfer operation, and transmits the transfer commands upon theinternal network transmission medium. Each transfer command directs anactivity associated with the movement of one or more work pieces (e.g.,semiconductor wafers) from the first fabrication area to the secondfabrication area.

The remote processors receive transfer commands via the internal networktransmission medium. Each remote processor addressed by a transfercommand produces one or more control signals in response to the transfercommand, and transmits the control signals upon the associated cellnetwork transmission medium. One or more transfer tools receive controlsignals via the cell network transmission medium. Each transfer tooladdressed by a control signal carries out one or more predefinedtransfer activities in response to the control signal. The end result ofthe coordinated actions of the transfer tools is movement of one or morework pieces from the first fabrication area to the second fabricationarea.

A The main processor maintains a database which includes entries foreach production unit (i.e., individual work piece or grouping of workpieces). Associated with each production unit is a location databaseentry indicating the fabrication area in which the production unit iscurrently located. Following the transfer of a production unit from onefabrication area to another, the main processor updates the locationdatabase entry associated with the production unit to indicate thefabrication area in which the production unit is currently located. Eachremote processor maintains a database which includes the operationalstatus of all transfer tools controlled by the remote processor.

The remote processors taking part in a transfer operation preferablyplan the portions of the transfer operation involving the transfer toolslocated within the corresponding fabrication areas. During suchplanning, the remote processors take into consideration, for example,the distance associated with each possible route, the amount of timerequired to complete the transfer along each possible route, and theutilization history of each transfer tool which may be involved in thetransfer. Weighing all such factors, the remote processors select thetransfer tools which will participate in the transfer operation.

The main processor also governs the dispersal of empty and non-emptycontainers within each fabrication area and among all of the fabricationareas. Empty and non-empty containers within a given fabrication areaare substantially evenly distributed between the stock areas within thefabrication area in order to reduce the total number of containers andthe required sizes of the respective empty and non-empty containerstorage areas within the stock areas. Movements of empty and non-emptycontainers are accomplished such that empty and non-empty containers donot accumulate within a small portion of the total number of fabricationareas.

In a transfer of a work piece residing within a container from the firstfabrication area to the second fabrication area through an air lockchamber, a first remote processor plans a first portion of the transferoperation involving transfer tools located within the first fabricationarea, and a second remote processor plans a second portion of thetransfer operation involving transfer tools located within the secondfabrication area. The first remote processor selects a first stock areawithin the first fabrication area which functions as the source of thework-piece-containing container. The second remote processor selects asecond stock area within the second fabrication area which functions asthe final destination of the work-piece-containing container. The firstremote processor directs the transport of the work-piece-containingcontainer to the first stock area, and the second remote processordirects any required prepositioning of an empty container within thesecond fabrication area. Following completion of the transfer, the mainprocessor updates one or more database entries associated with the workpiece to indicate the container number containing the work piece and toindicate that the container is located within the second fabricationarea.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a top plan view of one embodiment of the automated materialhandling system of the present invention, wherein the embodiment shownis an automated wafer transfer system including four air lock chambers,four robotic arms, and four stock areas;

FIG. 2 is a top plan view of a preferred embodiment of each air lockchamber of FIG. 1;

FIG. 3 is a top plan view of a preferred embodiment of each stock areaof FIG. 1; and

FIG. 4 is a block diagram of a preferred embodiment of a control systemof the embodiment of FIG. 1.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top plan view of one embodiment of an automated materialhandling system of the present invention. The embodiment shown is anautomated wafer transfer system 10 employed in a wafer fabricationfacility. Automated wafer transfer system 10 is used to performcontainerless transfer of semiconductor wafers through a wall 12 betweena first fabrication area 14 and a second fabrication area 16. Firstfabrication area 14 and second fabrication area 16 may have differentcontamination control requirements. First fabrication area 14 may be,for example, a photolithography processing area with stringentcontamination control requirements, and second fabrication area 16 maybe, for example, a chemical mechanical polish (CMP) processing area withmuch less stringent contamination control requirements. Advantages ofperforming wafer transfer operations automatically rather than manuallyinclude less variability in the amount of time required, lesscontamination introduced during the transfer operation, and lesspotential for wafer damage.

Automated wafer transfer system 10 includes four air lock chambers18a-d, four robotic arms 20a-d, four mass transfer systems 26a-d, fourrobotic arms 20a-d, four stock areas 22a-d, two transportation systems32a-b, and a control system (see FIG. 4). Each air lock chamber 18 ispositioned within a sealed opening in wall 12, and provides the abilityto transfer semiconductor wafers between first fabrication area 14 andsecond fabrication area 16. Containers 24a-d (e.g., wafer boats) areassociated with a given fabrication area and are used to transportsemiconductor wafers within that fabrication area. Air lock chambers18a-d include mass transfer systems 26a-d, respectively, which eliminatethe need to transfer containers with the wafers. Containers 24a-d thusremain within their respective fabrication areas during wafer transferoperations, and any contaminants clinging to containers 24a-d are nottransferred with the wafers from one fabrication area into the other. Inaddition, the air within each air lock chamber 18 is purged during wafertransfer operations, significantly reducing the number of airbornecontaminants transferred from one fabrication area into the other. Thusduring operation, each air lock chamber 18 provides a high level ofisolation between first fabrication area 14 and second fabrication area16.

Stock areas 22a-d are used to store containers. The containers mayeither be empty or contain wafers. Robotic arms 20a-d are positionedbetween air lock chambers 18a-d and stock areas 22a-d and are used totransfer containers between air lock chambers 18a-d and stock areas22a-d. Robotic arms 20a-b preferably move along a first set of parallelrails 30a, and robotic arms 20c-d preferably move along a second set ofparallel rails 30b.

Transportation system 32a is used to transport semiconductor waferswithin first fabrication area 14. Transportation system 32a includes atransport car 33a. Transport car 33a delivers containers to stock areas22a-b and receives containers from stock areas 22a-b. Transport car 33ais preferably mounted upon a first single rail 34a and moves along aclosed path within first wafer fabrication area 14. Similartransportation system 32b exists within second fabrication area 16, andincludes a transport car 33b. Transport car 33b preferably moves along asecond single rail 34b. Transport car 33b delivers containers to stockareas 22c-d and receives containers from stock areas 22c-d.

FIG. 2 is a top plan view of a preferred embodiment of each air lockchamber 18. Each air lock chamber 18 has two opposed operational sides36a-b. Operational side 36a is in first fabrication area 14 on one sideof wall 12, and operational side 36b is in second fabrication area 16 onthe other side of wall 12. A door 38a in operational side 36a allowsaccess to the interior of air lock chamber 18 from first fabricationarea 14, and a door 38b in operational side 36b allows access to theinterior of air lock chamber 18 from second fabrication area 16.

Air lock chambers 18a-d contain respective mass transfer systems 26a-d.Each mass transfer system 26 provides an automated means of unloadingsemiconductor wafers from containers and loading semiconductor wafersinto containers. Each mass transfer systems 26 includes a temporarystorage location for storing semiconductor wafers inside thecorresponding air lock chamber 18.

FIG. 3 is a top plan view of a preferred embodiment each stock area 22.Each stock area 22 includes an empty container storage area 40 and anon-empty container storage area 42. Each stock area 22 also has twoinput ports 44a-b and two output ports 46a-b on opposite sides. Eachstock area 22 also includes a transport system which transferscontainers between the ports (i.e., input ports 44a-b and output ports46a-b) and the container storage areas (i.e., empty container storagearea 40 and non-empty container storage area 42). Empty containers arestored in empty container storage area 40 and containers containingwafers are stored in non-empty container storage area 42. Containers arereceived by each stock area 22 at input ports 44a-b. Each input port 44has a sensor which senses the presence or absence of one or more waferswithin a received container. If the received container is empty, thecontainer is stored within empty container storage area 40 via thetransport system. If the received container contains one or more wafers,the received container is stored within non-empty storage area 42 viathe transport system. Upon request, containers stored within each stockarea 22 are provided at output ports 46a-b via the transport system.

FIG. 4 is a block diagram of a preferred embodiment of a control system48 of automated wafer transfer system 10. Control system 48 governs theoperations of the transfer tools of automated wafer transfer system 10.Control system 48 thus controls all movements of semiconductor wafersbetween first fabrication area 14 and second fabrication area 16.Control system 48 controls the operations of robotic arms 20a-d, airlock chambers 18a-d, mass transfer systems 26a-d, stock areas 22a-d, andtransportation systems 32a-b, via control signals. Robotic arms 20a-d,air lock chambers 18a-d, mass transfer systems 26a-d, stock areas 22a-d,and transportation systems 32a-b regularly report their operationalstatus to control system 48.

Control system 48 includes a main processor 50, two remote processors52a-b, an internal network transmission medium 56, a first cell networktransmission medium 58a, and a second cell network transmission medium58b. Main processor 50 is coupled to an external network transmissionmedium 54. External network transmission medium 54 is used to conveysignals. External network transmission medium 54 may be, for example, amulti-conductor cable, a coaxial cable, or a fiber-optic cable. Externalnetwork transmission medium 54 is part of an external network. Theexternal network may be, for example, a local area network (LAN) whichimplements the well known Ethernet communication protocol. A hostprocessor is also coupled to external network transmission medium 54.The host processor communicates and main processor 50 communicate withone another via external network transmission medium 54.

Main processor 50 is also coupled to an internal network transmissionmedium 56. Internal network transmission medium 56 is used to conveysignals, and may be, for example, a multi-conductor cable, a coaxialcable, or a fiber-optic cable. Internal network transmission medium 56is part of an internal network including main processor 50 and remoteprocessors 52a-b. The internal network may be, for example, acommunication system which implements the well known SECS IIcommunication protocol. Main processor 50 and remote processors 52a-bcommunicate with one another via external network transmission medium54.

Transfer tools located within first fabrication area 14 are coupled tofirst cell network transmission medium 58a, including transportationsystem 32a, stock areas 22a-b, and robotic arms 20a-b. Similarly,transfer tools located within second fabrication area 16 are coupled tosecond cell network transmission medium 58b, including transportationsystem 32b, stock areas 22c-d, and robotic arms 20c-d. Air lock chambers18a-d and corresponding mass transfer systems 26a-d are also coupled tofirst cell network transmission medium 58a. Cell network transmissionmedia 58a-b are used to convey signals. Each cell network transmissionmedium 58 may be, for example, a multiconductor cable, a coaxial cable,or a fiber-optic cable. Each cell network transmission medium 58 is partof a cell network. Each cell network may, for example, use digital logiclevel signals to convey commands and status information. Remoteprocessor 52a and transfer tools coupled to cell network transmissionmedium 58a communicate via cell network transmission medium 58a.Similarly, remote processor 52b and transfer tools coupled to cellnetwork transmission medium 58b communicate via cell networktransmission medium 58b.

Main processor 50 receives messages from the host computer via externalnetwork transmission medium 54. Such messages direct semiconductor wafertransfer operations. In response to messages from the host computerwhich direct wafer transfer operations, main processor 50 producestransfer commands, and transmits the transfer commands upon internalnetwork transmission medium 56. Remote processors 52a-b receive thetransfer commands, produce control signals in response thereto, andtransmit the control signals upon respective cell network transmissionmedia 58a-b. The transfer tools coupled to cell network transmissionmedia 58a-b receive the control signals and perform predefinedactivities in response to (i.e., execute) the control signals. The endresult of the coordinated activities of the transfer tools is a movementof one or more semiconductor wafers from one fabrication area toanother.

A typical transfer command is a `move request` command. Such a moverequest command identifies the work piece to be moved by identifying thecontainer containing the work piece. The move request also specifies thefinal destination of the container (i.e., the work piece).

Main processor 50 also governs the dispersal of empty and non-emptycontainers within each fabrication area and among all of the fabricationareas. Empty and non-empty containers within a given fabrication areaare substantially evenly distributed between the stock areas within thefabrication area in order to reduce the total number of containers andthe required sizes of the respective empty and non-empty containerstorage areas within the stock areas. Movements of empty and non-emptycontainers are accomplished such that empty and non-empty containers donot accumulate within a small portion of the total number of fabricationareas.

Main processor 50 also maintains a database 60 which includes databaseentries for each wafer lot. A number is assigned to each wafer lot, andcontainer database entries are associated with a wafer lot databaseentry indicting the container numbers of the one or more containerscontaining the wafers of the wafer lot. Each wafer-containing containerhas a location database entry indicating the fabrication area in whichthe container is currently located. Following the transfer of a waferlot from one fabrication area to another, main processor 50 updates theassociated container and location database entries. Remote processor 52amaintains a database 62 which includes the operational status of alltransfer tools controlled by remote processor 52a (i.e., robotic arms20a-b, air lock chambers 18a-d, mass transfer systems 26a-d, stock areas22a-b, and transportation system 32a). Remote processor 52b maintains adatabase 62 which includes the operational status of all transfer toolscontrolled by remote processor 52b (i.e., robotic arms 20c-d, stockareas 22c-d, and transportation system 32b).

An example will now be used to describe the transfer of a group ofsemiconductor wafers, lot number 123, arranged within a single containeridentified as container number 456. Main processor 50 sends a transfercommand to remote processors 52a-b directing the transfer of container456, containing lot number 123, from first fabrication area 14 to secondfabrication area 16. Remote processor 52a plans a first portion of thetransfer operation involving the transfer tools located within firstfabrication area 14, along with air lock chambers 18a-d and masstransfer systems 26a-d, and remote processor 52b plans a second portionof the transfer operation involving the transfer tools located withinsecond fabrication area 16. During the planning of such wafer transferoperations, remote processors 52a-b take into consideration, forexample, the distance associated with each possible route, the amount oftime required to complete the transfer along each possible route, andthe utilization history of each transfer tool which may be involved inthe transfer. Weighing all such factors, remote processor 52adetermines, for example, that stock area 22a, robotic arm 20a, and airlock chamber 18a with mass transfer system 26a will be involved in thetransfer operation. Similarly, remote processor 52b determines, forexample, that robotic arm 20c and stock area 22c will be involved in thetransfer operation.

Stock area 22a is to be the source of container 456 containing lotnumber 123, and stock area 22c is to be the final destination ofcontainer 456. Doors 38a-b of air lock chamber 18a are both closed atthe beginning of the transfer operation. Remote processor 52a issues acontrol signal to transportation system 32a directing the transport ofcontainer 456 to stock area 22a. Upon receipt of container 456 fromtransportation system 32a at an input port, stock area 22a notifiesremote processor 52a and stores container 456 within non-empty storagearea 42.

An empty container will be required to receive the wafers within secondfabrication area 16. If stock area 22c does not contain an emptycontainer, r emote processor 52b locates a suitable empty containerwithin second fabrication area 16 and sends a control signal totransportation system 32b causing transportation system 32b to deliverthe empty container to stock area 22c. Upon receipt of the emptycontainer from transportation system 32b at an input port, stock area22c notifies remote processor 52b and stores the empty container withinempty container storage area 40. Assume the empty container is number789.

Once stock area 22a has received container 456, remote processor 52aissues a control signal to stock area 22a which causes stock area 22a toprovide container 456 at an output port on a side of stock area 22aclosest to robotic arm 20a. Remote processor 52a sends a control signalto robotic arm 20a which causes robotic arm 20a to pick up container 456and place it within mass transfer system 26a of air lock chamber 18a.Remote processor 52a simultaneously sends a control signal to air lockchamber 18a which causes air lock chamber 18a to open door 38a inoperational side 36a, allowing access to the interior of air lockchamber 18a from first fabrication area 14. Once robotic arm 20a hasplaced the wafer-containing container within mass transfer system 26a,mass transfer system 26a removes the wafers from container 456 andplaces the wafers within the temporary storage location. Remoteprocessor 52a then sends a control signals to robotic arm 20a whichcauses robotic arm 20a to remove container 456, now empty, from air lockchamber 18a, and air lock chamber 18a closes door 38a in response to acontrol signal from remote processor 52a. Robotic arm 20a delivers emptycontainer 456 to an input port of stock area 22a closest to robotic arm20a. Stock area 22a stores empty container 456 within empty containerstorage area 40. Remote processor 52a reports completion of the firstportion of the transfer operation to main processor 50.

At this time doors 38a-b of air lock chamber 18a are both in the closedposition. A period of time is allowed to elapse during which all of theair present within air lock chamber 18a is exhausted and replaced byfiltered air provided, for example, through the upper surface of airlock chamber 18a. This purging step helps prevent any airbornecontaminants introduced into air lock chamber 18a from first fabricationarea 14 when door 38a was open from being transferred to secondfabrication area 16 when door 38b is subsequently opened.

During the time the air within air lock chamber 18a is being purged,main processor 50 sends a transfer command to remote processor 52b whichinitiates the second portion of the transfer operation. Remote processor52b sends a control signal to stock area 22c causing stock area 22c toprovide empty container 789 at an output port on a side of stock area22c closest to robotic arm 20c. Remote processor 52b then sends acontrol signal to robotic arm 20c which causes robotic arm 20c to pickup empty container 789 and place it within mass transfer system 26a ofair lock chamber 18a. Remote processor 52a simultaneously sends acontrol signals to air lock chamber 18a causing air lock chamber 18a toopen door 38b in operational side 36b, allowing access to the interiorof air lock chamber 18a from second fabrication area 16. Once roboticarm 20c has placed empty container 789 within mass transfer system 26a,mass transfer system 26a removes the wafers from the temporary storagelocation and places the wafers within container 789. Remote processor52b then sends a control signal to robotic arm 20c causing robotic arm20c to remove container 789, now containing the wafers, from air lockchamber 18a, and door 38b is closed. Remote processor 52b then sends acontrol signal to robotic arm 20c causing robotic arm 20c to delivercontainer 789, containing lot number 123, to an input port of stock area22c closest to robotic arm 20c. Stock area 22c stores thewafer-containing container within non-empty storage area 42.

At this time remote processor 52b reports completion of the secondportion of the transfer operation to main processor 50. Main processor50 updates database 60 in light of the completed transfer operation. Thecontainer and location database entries associated with lot number 123are updated to reflect that container 789 now contains wafer lot 123,and that container 789 is currently located in second fabrication area16.

It is noted that four air lock chambers 18a-d are available for wafertransfer operations. Control system 48 is capable of controlling wafertransfer operations involving multiple air lock chambers in order toimprove the number of wafers transferred in a given period of time(i.e., wafer transfer throughput). For example, multiple containers maybe transferred from first fabrication area 14 to second fabrication area16 using stock areas 22a and 22c, robotic arms 20a and 20c, and air lockchambers 18a and 18b with respective mass transfer systems 26a and 26b.Following transfer of wafers within a first wafer-containing containerto mass transfer system 26a of air lock chamber 18a, robotic arm 20a mayplace a second wafer-containing container within mass transfer system26b of air lock chamber 18b while the air within air lock chamber 18a isbeing purged. As a result, the number of wafers transferred in a givenamount of time is increased. Additional wafer transfer tools (i.e.,stock areas 22b and 22d, robotic arms 20b and 20d, and air lock chambers18b and 18d with respective mass transfer systems 26b and 26d) may alsobe employed in order to increase wafer transfer throughput.

Control system 48 is also capable of carrying out wafer transferoperations in "degraded" modes when one or more of the wafer transfertools are inoperative. For example, if robotic arm 20a is inoperative,remote processor 52a may direct robotic arm 20b to accomplish allcontainer transfers between stock areas 22a-b and air lock chambers18a-d. If robotic arms 20a-b are both inoperative, remote processor 52ais able to coordinate wafer transfer operations involving the manualtransfer of wafers between stock areas 22a-b and air lock chambers18a-18d.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this invention is believed to be an automatedmaterial handling system for a manufacturing facility divided intoseparate fabrication areas. The automated material handling system plansand carries out the movement of work pieces between fabrication areasand maintains a database indicating the location of the work pieceswithin the manufacturing facility. Furthermore, it is also to beunderstood that the form of the invention shown and described is to betaken as exemplary, presently preferred embodiments. Variousmodifications and changes may be made without departing from the spiritand scope of the invention as set forth in the claims. It is intendedthat the following claims be interpreted to embrace all suchmodifications and changes.

What is claimed is:
 1. A material handling system, comprising:a mainprocessor configured to produce a transfer command, wherein the transfercommand directs the movement of a work piece from a first fabricationarea to a second fabrication area; a remote processor coupled to receivethe transfer command and configured to respond to the transfer commandby: (i) selecting a target transfer tool from among a plurality oftransfer tools, and (ii) producing a control signal directed to thetarget transfer tool; and wherein the target transfer tool is coupled toreceive the control signal and configured to execute the control signal.2. The material handling system as recited in claim 1, wherein the workpiece comprises a semiconductor wafer.
 3. The material handling systemas recited in claim 1, wherein the transfer command identifies the workpiece.
 4. The material handling system as recited in claim 1, whereinthe target transfer tool is a stock area within the first fabricationarea which is to serve as a source of the work piece.
 5. The materialhandling system as recited in claim 1, wherein the target transfer toolis a stock area within the second fabrication area which is to serve asa final destination for the work piece.
 6. The material handling systemas recited in claim 1, wherein the plurality of transfer tools includesa transportation system, a stock area, a robotic arm, an air lockchamber, and a mass transfer system.
 7. The material handling system asrecited in claim 1, further comprising an internal network transmissionmedium, wherein internal network transmission medium is used to conveyelectrical signals, and wherein the main processor and the remoteprocessor are coupled to the internal network transmission medium andcommunicate via the internal network transmission medium.
 8. Thematerial handling system as recited in claim 7, wherein the internalnetwork transmission medium is selected from the group consisting of amulti-conductor cable, a coaxial cable, and a fiber-optic cable.
 9. Thematerial handling system as recited in claim 1, further comprising acell network transmission medium, wherein the cell network transmissionmedium is used to convey electrical signals, and wherein the remoteprocessor and the target transfer tool are coupled to the cell networktransmission medium and communicate via the cell network transmissionmedium.
 10. The material handling system as recited in claim 9, whereinthe network transmission medium is selected from the group consisting ofa multi-conductor cable, a coaxial cable, and a fiber-optic cable.
 11. Amaterial handling system, comprising:a main processor configured toproduce a transfer command, wherein the transfer command directs themovement of a work piece from a first fabrication area to a secondfabrication area; a first remote processor coupled to receive thetransfer command and configured to produce a first control signal inresponse to the transfer command; a second remote processor coupled toreceive the transfer command and configured to produce a second controlsignal in response to the transfer command; a first transfer toolcoupled to receive the first control signal and configured to executethe first control signal; and a second transfer tool coupled to receivethe second control signal and configured to execute the second controlsignal.
 12. The material handling system as recited in claim 11, whereinthe first transfer tool is located within the first fabrication area andselected from the group consisting of a transportation system, a stockarea, and a robotic arm.
 13. The material handling system as recited inclaim 11, wherein the second transfer tool is located within the secondfabrication area and selected from the group consisting of atransportation system, a stock area, and a robotic arm.
 14. A materialhandling system, comprising:an internal network transmission medium forconveying communication signals; a main processor coupled to theinternal network transmission medium and configured to produce atransfer command upon the internal network transmission medium, whereinthe transfer command directs the movement of a work piece from a firstfabrication area to a second fabrication area; a cell networktransmission medium for conveying control signals; a remote processorcoupled between the internal and cell network transmission media,wherein the remote processor is configured to receive the transfercommand and to produce a control signal upon the cell networktransmission medium in response to the transfer command; and a transfertool coupled to the cell network transmission medium, wherein thetransfer tool is configured to receive and execute the control signal.15. The material handling system as recited in claim 14, wherein thetransfer tool is selected from the group consisting of a transportationsystem, a stock area, a robotic arm, an air lock chamber, and a masstransfer system.
 16. A material handling system, comprising:a mainprocessor configured to produce a transfer command, wherein the transfercommand directs the movement of a work piece from a first fabricationarea to a second fabrication area, wherein the first fabrication area isisolated from the second fabrication area by an airlock chamber; aremote processor coupled to receive the transfer command and configuredto produce a control signal in response to the transfer command; and atransfer tool coupled to receive the control signal and configured toexecute the control signal.
 17. The material handling system as recitedin claim 16, wherein the work piece comprises a semiconductor wafer. 18.The material handling system as recited in claim 16, wherein thetransfer command identifies the work piece.
 19. The material handlingsystem as recited in claim 16, wherein the remote processor selects astock area within the first fabrication area which is to serve as asource of the work piece.
 20. The material handling system as recited inclaim 16, wherein the remote processor selects a stock area within thesecond fabrication area which is to serve as a final destination for thework piece.
 21. The material handling system as recited in claim 16,wherein the transfer tool is selected from the group consisting of atransportation system, a stock area, a robotic arm, an air lock chamber,and a mass transfer system.
 22. The material handling system as recitedin claim 16, further comprising an internal network transmission medium,wherein internal network transmission medium is used to conveyelectrical signals, and wherein the main processor and the remoteprocessor are coupled to the internal network transmission medium andcommunicate via the internal network transmission medium.
 23. Thematerial handling system as recited in claim 22, wherein the internalnetwork transmission medium is selected from the group consisting of amulti-conductor cable, a coaxial cable, and a fiber-optic cable.
 24. Thematerial handling system as recited in claim 16, further comprising acell network transmission medium, wherein the cell network transmissionmedium is used to convey electrical signals, and wherein the remoteprocessor and the transfer tool are coupled to the cell networktransmission medium and communicate via the cell network transmissionmedium.
 25. The material handling system as recited in claim 24, whereinthe network transmission medium is selected from the group consisting ofa multi-conductor cable, a coaxial cable, and a fiber-optic cable.
 26. Amaterial handling system, comprising:a main processor configured toproduce a transfer command, wherein the transfer command directs themovement of a work piece from a first fabrication area to a secondfabrication area; a remote processor coupled to receive the transfercommand and configured to produce a control signal in response to thetransfer command; a transfer tool coupled to receive the control signaland configured to execute the control signal; and an internal networktransmission medium, wherein the internal network transmission medium isused to convey electrical signals, and wherein the main processor andthe remote processor are coupled to the internal network transmissionmedium and communicate via the internal network transmission medium. 27.The material handling system as recited in claim 26, wherein the workpiece comprises a semiconductor wafer.
 28. The material handling systemas recited in claim 26, wherein the transfer command identifies the workpiece.
 29. The material handling system as recited in claim 26, whereinthe remote processor selects a stock area within the first fabricationarea which is to serve as a source of the work piece.
 30. The materialhandling system as recited in claim 26, wherein the remote processorselects a stock area within the second fabrication area which is toserve as a final destination for the work piece.
 31. The materialhandling system as recited in claim 26, wherein the transfer tool isselected from the group consisting of a transportation system, a stockarea, a robotic arm, an air lock chamber, and a mass transfer system.32. The material handling system as recited in claim 26, wherein theinternal network transmission medium is selected from the groupconsisting of a multi-conductor cable, a coaxial cable, and afiber-optic cable.
 33. The material handling system as recited in claim26, further comprising a cell network transmission medium, wherein thecell network transmission medium is used to convey electrical signals,and wherein the remote processor and the transfer tool are coupled tothe cell network transmission medium and communicate via the cellnetwork transmission medium.
 34. The material handling system as recitedin claim 33, wherein the cell network transmission medium is selectedfrom the group consisting of a multi-conductor cable, a coaxial cable,and a fiber-optic cable.
 35. A material handling system, comprising:amain processor configured to produce a transfer command, wherein thetransfer command directs the movement of a work piece from a firstfabrication area to a second fabrication area; a remote processorcoupled to receive the transfer command and configured to produce acontrol signal in response to the transfer command; a transfer toolcoupled to receive the control signal and configured to execute thecontrol signal; and a cell network transmission medium, wherein the cellnetwork transmission medium is used to convey electrical signals, andwherein the remote processor and the transfer tool are coupled to thecell network transmission medium and communicate via the cell networktransmission medium.
 36. The material handling system as recited inclaim 35, wherein the work piece comprises a semiconductor wafer. 37.The material handling system as recited in claim 35, wherein thetransfer command identifies the work piece.
 38. The material handlingsystem as recited in claim 35, wherein the remote processor selects astock area within the first fabrication area which is to serve as asource of the work piece.
 39. The material handling system as recited inclaim 35, wherein the remote processor selects a stock area within thesecond fabrication area which is to serve as a final destination for thework piece.
 40. The material handling system as recited in claim 35,wherein the transfer tool is selected from the group consisting of atransportation system, a stock area, a robotic arm, an air lock chamber,and a mass transfer system.
 41. The material handling system as recitedin claim 35, further comprising an internal network transmission medium,wherein internal network transmission medium is used to conveyelectrical signals, and wherein the main processor and the remoteprocessor are coupled to the internal network transmission medium andcommunicate via the internal network transmission medium.
 42. Thematerial handling system as recited in claim 41, wherein the internalnetwork transmission medium is selected from the group consisting of amulti-conductor cable, a coaxial cable, and a fiber-optic cable.
 43. Thematerial handling system as recited in claim 35, wherein the cellnetwork transmission medium is selected from the group consisting of amulti-conductor cable, a coaxial cable, and a fiber-optic cable.